Radio direction-finding (DF) or determining the angles of arrival (AOA) of multiple simultaneous radio frequency (RF) cochannel signals in an inexpensive manner is a capability that is currently not found in existing implementations. In an RF environment, cochannel signals are two or more signals transmitted on the same carrier frequency at the same time. Generally, conventional direction-finding approaches fall into two broad categories.
The first category includes expensive, highly capable systems, which can locate multiple sources, but which require multiple phase coherent downconversion and sampling channels. Examples of these approaches include subspace based methods such as the MUSIC (multiple signal classification) algorithm, which capitalizes on the linear independence among multiple signals from different directions, thereby providing totally robust performance in complex signal environments. Another such example is a computed-interferometry radar system with coherent integration, as discussed in U.S. Pat. No. 4,992,796, which is herein incorporated by reference in its entirety.
The second category includes relatively inexpensive, single channel systems. With these approaches, multiple antennas are sampled at a high rate in a commutated fashion, and the induced phase changes gives an indication of the AOA. However, systems of this type can only locate a single source and cannot operate in the presence of cochannel interference or jamming.
What is needed, therefore, are techniques for cost effective radio direction-finding for environments with cochannel signals.